The present invention relates to a belt drive system. More particularly, it relates to a belt drive system which comprises a toothed belt having cut grooves in the teeth in the longitudinal direction of the belt and toothed pulleys having one or more ribs, to engage with the cut grooves in the belt teeth, on the surface of the pulley body of each pulley.
Generally, the toothed belt in the belt drive system comprising mainly a belt and pulleys has a plurality of equally spaced teeth, in the longitudinal direction of the belt, on the surface of the belt body which includes tensile members therein. The surface of the toothed belt is covered with rubber cloth or treated with elastomers such as polyurethane which are excellant in wear-resistance. As shown in FIG. 1(a), the surfaces 101 and 102 of the conventional toothed belt 100 are smooth. When the toothed belt engages with toothed pulleys, the bottom of the tooth cavity 102 of the belt teeth comes into contact with the exterior surface of the pulley teeth, resulting in plosive sounds of compressed air caused by a sudden discharge of the compressed air from spaces between the belt teeth and the pulley teeth when the belt engages with the pulley. As the engagement of the belt with pulleys is carried out at higher speed, the plosive sounds become louder.
The conventional toothed belt is inferior in durability because the bottom of the tooth cavities wears considerably when it comes into contact with the pulley teeth. In order to reduce the wear of the bottom of the belt tooth cavities, it is necessary to enlarge the bottom area of the belt tooth cavities thereby minimizing the belt contact pressure per unit area of the pulley surface. However, the theoretical tooth width (i.e. the length of the tooth base in the longitudinal direction of the belt) must be wider to insure that the toothed belt has strong and wear-resistant belt teeth. As a result, the conventional toothed belt provides for a large bottom area of the belt tooth cavacities but narrow width: that is, the wear-resistance of the belt is considered more important than the tooth strength. Thus, most conventional toothed belts have a weakness in tooth strength and cannot be applied to a cam shaft drive of large vehicles such as trucks and buses requiring a large capacity belts.
Moreover, the toothed belt tends to move in a zigzag direction or slip sideways during belt drive, resulting in a heat generation and/or belt wear. Such belt slippage may be reduced by flanges to be disposed on the pulleys. However, a substantial area of the pulleys in contact with the belt is reduced by these flanges, thereby decreasing the belt capacity.
The flanges are essential to the conventional pulleys, so that the configuration of the pulleys is complicated and low priced production of pulleys having a consistant quality is not easy.
U.S. Pat. No. 2,988,925 discloses such a toothed belt 103 as shown in FIG. 1(b), wherein narrow and shallow grooves 105 are disposed in the top of the teeth 104, along the length of the teeth 104. Publication of Japanese Application for patent (Tokkyo-Kokoku) No. 47-34433 (34433/1972) discloses such a pulley 106 as shown in FIG. 1(c), wherein a plurality of narrow and shallow grooves 108 are disposed in the pulley teeth 107 in the longitudinal direction with respect to a belt which engages with this pulley. Alternatively the grooves are helically disposed in the pulley teeth. Both of the above prior arts are aimed only at reducing the plosive sounds occuring during engagement of the toothed belts with the toothed pulleys, but never simultaneously solve the problems of both the zigzag movement or slide of the belt on the pulley and the resulting heat-generation and belt-wear.
Moreover, toothed belts are used as timing transmission belts transmitting power by means of engagement with pulley teeth, while V-belts are used for transmitting power by means of frictional force generated between the V-belts and pulleys. Both belts are of a different nature. Thus, it has been understood by those skilled in the art that a combination of concept and function of both toothed belts and V-belts would be senseless and unpractical.